MARS ROVER DIGS IN; SOJOURNER BEAMS FIRST DATA FROM DUSTY SURFACE.

Byline: John Noble Wilford The New York Times

The roving vehicle Sojourner, the first mobile explorer of another planet, began prospecting the soil and rocks of Mars on Sunday and transmitting a flood of data to overjoyed scientists, their dreams of knowing what Mars is made of about to come true.

As its first task, Sojourner pressed the head of its principal scientific instrument to the powdery surface at the base of the Mars Pathfinder landing craft. The readings from this first examination of the chemical composition of Mars were radioed to Earth on Sunday afternoon for analysis by geologists.

Then Sojourner, which is about the size of a microwave oven, prepared to crawl a few feet to begin a 10-hour study of a pitted, knobby rock that geologists are calling ``Barnacle Bill.''

``We have a fully functional spacecraft,'' Matthew Golombek, the chief project scientist, said. ``Everything is working just perfectly.''

Overcoming communications trouble and other setbacks, the Sojourner left the Pathfinder lander Saturday shortly before 11 p.m. PDT. The robotic rover's six metal wheels rolled hesitantly down a ramp, reminding flight controllers of another July, in 1969, when Neil Armstrong descended the Apollo 11 ladder for the first ``giant leap'' on the moon.

When Sojourner came to a stop on the surface, Richard Cook, the mission manager here at the Jet Propulsion Laboratory, set off cheers in the control room with the announcement: ``The rover is on the surface of Mars. We've got some great images back, and all the scientists are in heaven.''

As they studied the panoramic views of the landing site produced by Pathfinder's color camera, scientists got a clearer picture of what Mars looks like up close on the flood plain of Ares Vallis, near ancient highlands. They could hardly wait for Sojourner to navigate the field of rocks and drift sand out to larger boulders and hills in the distance.

At a news conference, Dr. Dan Britt, a geologist at the University of Arizona at Tucson, echoed the excitement and anticipation of the project's science team. ``We've got a cornucopia of rocks and processes,'' he said.

Dr. Ronald Greeley, a planetary geologist at Arizona State University in Tempe, said, ``We chose this site because we wanted to see geological diversity on Mars, and we have not been disappointed.''

In all directions from Pathfinder, scientists could see rocks: small and large, rounded and jagged and blocky, some coated with rust-colored dust and others bare and gray. The more rounded ones appeared to have been eroded as they tumbled from the highlands in ancient floods. One rock is large and dark, resembling a sleeping bear; with their penchant for nicknames, geologists are calling it ``Yogi.''

A study of the rounded rocks, Greeley said, could enable geologists to determine the amount of water that carried them from the highlands to the plain. ``Their appearance is definitely consistent with transport by water,'' he said.

The blocky rocks - one is rectangular, like a solid stone table, and another looks like a couch - could be bedrock ejected when an asteroid gouged out the crater less than a mile from the lander, geologists said. The crater's rim is barely visible.

Two hills, each several hundred feet high, stand out about a mile to the southwest. Scientists are calling them ``Twin Peaks.'' What looks like a white stripe runs down the slope of one hill. Scientists call it the ``ski run,'' but they think it is probably wind-blown soil drifting downslope.

Of particular interest are apparent horizontal bands on the face of one hill, which could be evidence of sediments laid down by ancient flooding.

There is no liquid water on the Martian surface now, but scientists figure that the planet is water-rich. Vast amounts of frozen water exist in the north polar cap and beneath the surface as permafrost, and some liquid water might lie at greater depths. Judging from pictures of Mars returned by the two Viking orbiters in 1976, water washed vast expanses of the landscape several billion years ago, carving wide channels like Ares Vallis. Rocks from that time and place, scientists suspect, could contain evidence of that warmer, wetter environment - a time when life might have gotten a start on Mars.

The broad bands reminded Greeley of the walls of the Grand Canyon. They could be layers of rocks and soil deposited in successive periods of flooding, he said. Or they could be terraces cut by erosion or sediments banked against the side of the hill.

Pathfinder's meteorological instruments have begun sending weather reports from the site. As expected, the place is no vacation paradise. Tim Schofield of the Jet Propulsion Laboratory said the warmest noontime temperatures were 8 degrees below zero Fahrenheit. Light winds were blowing out of the west, with an occasional cold gust from the southwest. At each gust, temperatures plunged at least 30 degrees.

Dust storms in the Martian southern hemisphere, as observed recently by the Hubble Space Telescope, have not reached Ares Vallis, which is about 19 degrees north of the equator. Skies there are clear.

The scientists reported high public interest in the images and information about the project made available on the Internet. They said that the number of visits to Pathfinder Internet sites was so heavy - one scientist said that there had been 100 million visits, or ``hits'' - that the Jet Propulsion Laboratory had added another site to help handle the load.

The project scientists were able to turn their attention to the sights of Mars and prospects of discovery because engineers had managed to solve two problems that for a time threatened the mission's full success. After Pathfinder landed on Friday, pictures revealed that a deflated air bag, one of several used to cushion the landing, was bunched up near the rover. It could have been an obstacle to the rover's rollout.

The flight controllers sent commands for Pathfinder to lift the metal base holding the rover and pull part of the air bag under, and out of the way. But then another, more perplexing malfunction cropped up.

Late Friday, the radio link between the rover and Pathfinder became erratic. Some signals were getting through, but the flow was intermittent. Without clear communications to Pathfinder, Sojourner would not be able to operate on the surface and return its scientific findings. The rover was not built to communicate directly to Earth. For a time, flight controllers were not sure when, or if, they would be able to get Sojourner up and running.

By Saturday afternoon, however, the problem went away. Sojourner was talking to Pathfinder. Engineers are still not sure what caused the communications lapse or how it was corrected. They had sent commands for several possible fixes, but it was also possible, they said, that the rover had somehow healed itself.

CAPTION(S):

2 Photos

PHOTO (1 -- color) Brian Cooper, who drives the Mars rover Sojourner from his Pasadena desk, shows the vehicle he is commanding to travel the planet's surface Sunday.

(2) This image from the Mars Pathfinder shows two rocks that have intrigued scientists. ``Barnacle Bill,'' on the near left, and the larger, bear-like ``Yogi'' may hold clues to the planet's history.

Associated Press